charts for future task runtime statistics;

Isabelle-hg: http://isabelle.in.tum.de/repos/isabelle@50980 bc746aa3e8d5207e51c47d6dfe24b08d2e9557ea
tuned signature;

Isabelle-hg: http://isabelle.in.tum.de/repos/isabelle@50981 1791a90a94fbcc7967aba53a83c198d6b5ab3b60
use inlined session name as title for charts;
tuned signature;

Isabelle-hg: http://isabelle.in.tum.de/repos/isabelle@50982 a7aa17a1f721284794128e5c3e157006db908be9
accomodate scala-2.9.2;

Isabelle-hg: http://isabelle.in.tum.de/repos/isabelle@50989 a7f6ce0493b78b1a6eaf4c2cb686d4b82d9fab76